The catalytic distillation technique is to carry out reaction of reactants and separation of products in the same catalytic distillation apparatus, while the reaction(s) is being carried out, the formed product is separated out simultaneously, thereby the reaction equilibrium will be broken through continuously, making the reaction toward completion and increasing the conversion of reactants. Furthermore, as the reaction heat is absorbed by vaporizing some of the components, not only the reaction temperature will be kept constant and the energy consumption of the process reduced significantly, but also the technological process will be simplified and the investment reduced greatly. Generally, the catalytic distillation column consists of three sections: a rectification section at the upper part, a catalytic reaction section at the middle part and a stripping section at the lower part of the column. In the catalytic distillation column, the downward flowing liquid stream and upward flowing vapor stream must flow countercurrently through the catalytic reaction section at the middle part to carry out reaction of reactants and fractionation of products simultaneously therein. However, the particle size of conventional catalysts is too small, the flow resistance in the catalyst beds will be even so high as to make the downward flowing liquid and the upward flowing vapor streams difficult to pass countercurrently through the reaction section at the middle part of the column, and consequently make the equipment impossible to run normally and the reaction of reactants and fractionation of products impossible to be carried out simultaneously.
In order to solve the problems aforesaid, some catalytic distillation equipments or methods for packing catalyst have been reported in literatures. For example, U.S. Pat. No. 4,471,154 proposes to use catalyst packed in capsules, made of fabrics or stainless-steel mesh which are permeable to liquid but impermeable to catalyst particles, then these capsules are disposed on fractionating trays in the reaction section at the middle part of the column to have the reactants diffusing into the capsules, contacting with the catalyst and taking part in reaction when they flow across the trays. But the catalyst inventory of this structure is limited. U.S. Pat. No. 4,215,011 discloses a method of with catalyst packed in a number of bags, and the catalyst bags are placed in said reaction section at the middle part of the column, having certain gap between the bags to allow liquid and vapor streams to pass countercurrently through said reaction section. U.S. Pat. No. 3,579,309 discloses a structure wherein a number of small reactors are arranged outside the column, liquid stream flows from an upper tray through the small reactor outside the column and then back into next tray. Thus the structure is complicated and the flow resistance of fluid is still high. In U.S. Pat. No. 3,634,534, the catalyst is placed in downcomers of the trays, the inventory of catalyst is limited significantly. Besides, there are also other similar structures, but some of them are either complicated structures, or in some others the amount of catalyst is limited, or in some the reaction efficiency is influenced due to the use of catalyst packed in small fabric capsules, thus not only the reactants have to diffuse into the small capsules to contact with catalyst and undergo reaction, but also the products have to diffuse out therefrom after reacting.
U.S. Pat. No. 5,523,061 discloses a structure in which the catalyst is packed into a number of overlapping-arranged fixed beds, between two adjacent beds conventional trays is disposed, thus, only the liquid stream can pass through the catalyst bed and undergo reaction, and the mass transfer and heat exchange can carry out on the trays between the vapor stream passing through the vapor channel and the liquid stream coming from the upper catalyst bed. Since the vapor stream can not contact with the catalyst directly, the reaction efficiency is affected. In the invention of CN 1065412A, the catalyst is placed between ripple packings, the structure is complicated.
It is proposed in U.S. Pat. No. 4,250,052 that the packing type sulphonated resin catalyst with an inert skeleton is prepared by dissolving, at first, a vinyl aromatic polymer or copolymer in a solvent, coating the substrate of conventional distillation packing with the resulting solution, then sulphonating the coated packing. However, the content of active component in the catalyst prepared by this process is low, and also the apparatus utilization coefficient is low; especially, the problems such as stripping and peeling off the active components from the substrate and so on are resulted owing to different rates of expansion, swelling and shrinkage between the substrate and active components, and changes of other environmental factors such as temperature and medium and the like. In U.S. Pat. No. 4,194,964, it is described only that the catalyst can be made into conventional shapes of packing, for instance, Raschig rings, Pall ring and rectangular saddle shape and the like, but not any method of preparation is described, moreover, the external surface area of the Raschig rings is small, separation efficiency and reaction efficiency are low, and its strength is also weak; it is difficult to mould the catalyst materials into other shapes. U.S. Pat. No. 5,235,102 proposes that the catalyst is prepared as beehive-shaped regular packing having 5-1000 cells, preferably 100-200 cells per square inch. But the flow resistance over this catalyst is high because of its small pore channel; furthermore, it requires that a worker should enter the column to arrange this regular shaped packing one by one, manually, in a vertical position, and that the deactivated catalyst packing should be removed in the same way; such operation is arduous, and the residual organic material in the column is harmful to human body. The disclosure of CN 1060228A is mainly that the active components of catalyst are made into a tray, but in doing so there are great difficulties technologically, besides the catalytic surface area contacting with the reaction stream is very limited. The patent also proposes to make the catalyst into Raschig rings, vehicle wheel shape, Pall rings, rectangular saddles, spherical or cylindrical shapes, or the regular packings of ripple shape or beehive shape. However, the Raschig rings, which have low external surface area and weak strength, are unfavourable to the reaction and fractionation; wheel shaped catalyst has low external surface area and low allowable flow flux of vapor and liquid; Pall rings and rectangular saddle shape are difficult to be moulded directly with the catalyst materials; the spherical and cylindrical catalysts have too small free space formed in the beds and higher flow resistance to allow the vapor and liquid stream passing countercurrently through the reaction section; as for said ripple or beehive shaped regular packings, they also need to be loaded and unloaded manually in the column, and they are also difficult to be made with the catalyst materials directly. GB 2193907 discloses a hollow catalyst with external ribs characterized in that the external ribs are arranged to avoid the adjacent catalyst pellets interlocking each other, for use in tubular reactor for conducting gas phase reaction such as the steam conversion and oxidation in order to improve the distribution of fluid and reduce the pressure drop. Even though it is used as a dual function catalyst in the catalytic distillation, the hollow shaped catalyst is unfavourable for increasing the efficiency of reaction and fractionation owing to its small external surface area.